[RASMB] smaller protein size than expected

[Dmitry Veprintsev]

Dear Fang,
I so similar behavior when the protein was degraded, or when the user
provided wrong sequence (or forgot to subtract the tag). Mass-spec is a
good way of checking if there is any degradation of the sample, and if
it is the right protein.
The other reason could be unusually dense buffer, but it is unlikely to
explain such a big difference.
best regards, Dmitry

fang.yi at yale.edu wrote:
> hello all,
> 
> I recently did sedimentation equilibrium runs on a protein (monomer
> size: 16
> KD), at 3 concentrations (260, 130, 52 u M) at speeds of 25, 30, 35000 RPM.
> Using Heteroanalysis, I could only fit the data into an ideal solution
> model,
> with a monomer MW of 10KD.  Also, this protein runs at a MW lower than
> expected
> on the gel filtration col also. SDS gel indicates it's the right size
> and not
> degraded after the measurements.
> 
> Anybody has any suggestions why this protein appears to be such a "smaller"
> protein?
> 
> Thanks a lot,
> 
> Fang Yi
> Postdoc Fellow
> Yale University
> Molecular Biophysics and Biochemistry
> New haven, CT 06511
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> 

-- 
Dr. Dmitry Veprintsev
MRC Centre for Protein Engineering
Hills Road, Cambridge CB2 2QH, UK